This invention relates to an integrated circuit. In particular, this invention relates to an integrated circuit including at least one environmental sensor. The invention further relates to a method of making such an integrated circuit.
Nowadays, integrated circuits may comprise a plethora of different sensors, such as ambient light (AL) sensors, temperature (T) sensors, pressure sensors, gas sensors, relative humidity (RH) sensors, specific analyte detection sensors, and so on.
Integrated circuits of this kind have a wide range of applications. For example, they can be used in the field of supply chain management to track and monitor the freshness of food and beverages. They can also be used as environmental sensors, for example as part of a heating, ventilation and air conditioning (HVAC) system in an automobile or in a building (e.g. a Smart Building). Additional applications include those in agricultural (e.g. the sensing of environmental conditions in greenhouses) or in medical fields. Their provision in mobile communications devices such as mobile telephones, tablets or laptops can also enable a wide range of further applications that require measurements of local environmental factors.
The provision of sensors in integrated circuits of this kind allows devices to be produced that have a small form factor. For example, due to their small form factor, integrated circuits incorporating one or more sensors can be included in Radio Frequency Identification (RFID) tags, allowing for easy programming and readout.
Moreover, it allows large numbers of sensors to be manufactured cheaply, using established semiconductor processing techniques.
An example of an integrated circuit including an environmental sensor is illustrated in FIG. 1A. FIG. 1B shows a cross section of the integrated circuit shown in FIG. 1A.
The integrated circuit includes a semiconductor substrate 2 having a major surface 10. The environmental sensor 6 is provided on the major surface 10. Other components may typically also be proved in the substrate 2, such as memory 14, control circuitry 16 and an analogue to digital converter (ADC) 18. Additionally, a number of bond pads can be provided on the major surface 10, to allow connections to be made to the substrate 2 using traditional wire bonding processes.
The integrated circuit further includes an encapsulant 4. The encapsulant 4 takes the form of a protective layer that encloses the substrate 2, covering most of the major surface 10. As shown in FIG. 1, the encapsulant 4 covers features such as the memory 14, control circuitry 16 and ADC 18. However, environmental sensors such as pressure sensors or gas sensors require direct access to the environment surrounding the integrated circuit to perform their sensing function. For this reason, the environmental sensor 6 is located in an opening 8 which is provided in the encapsulant 4.
The encapsulant 4 can be formed on the substrate 2 using a process known as foil assisted moulding (FAM). In this process, a pattern covered with a foil is pressed down over the major surface 10 of the substrate 2. Encapsulant 4 is then injected into the space around the substrate, including the area between the foil and the major surface 10. The pattern is profiled to allow the encapsulant 4 to cover substantially all of the major surface 10, while leaving an opening 8 at a position corresponding to the environmental sensor 6.
This approach to packaging an integrated circuit including an environmental sensor suffers from a number of disadvantages. For example, when using the foil assisted moulding process, it is difficult to control the exact position of the opening 8. Because of this lack of positional accuracy, a relatively large portion of substrate cannot be used. Also, since the environmental sensor 6 is left exposed throughout the manufacturing process, delicate features of the sensor (such as the deflectable membrane of a pressure sensor or the suspended resistive wire of a thermal conductivity based CO2 sensor) may be damaged. These delicate features may particularly be damaged during the FAM process, during which the substrate 2 and the components provided thereon are subjected to high levels of physical stress. Damage may also occur after manufacture. Moreover, since the environmental sensor is completely exposed, it is prone to an accumulation of dust entering the opening 8.
Packages formed using the above described process are also typically expensive and are also physically large, owing in part to the large form factor of the encapsulant 4 and the large casing in which the encapsulated substrate 2 is mounted.